Amplitude modulated pulse translating circuits



March'z, Y1954 M, SCOTT 2,673,330

AMPLITUDE MODULATED PULSE TRANSLTING CIRCUITS Filed De@ 25, 1952 Y I I UL] mi!! I INVENTOR.

(a.)V '707 l fai (e) Hamann M SEDIT Mffm TTORNEY Patented Mar. 23, 1954AMPLITUDE MODULATED PULSE TRANSLATING CIRCUITS Howard Mulder Scott,Philadelphia, Pa., assignor to Radio Corporation of America, acorporation of Delaware Application December 23, 1952, Serial No.327,485

10 Claims.

The invention relates to pulse translating circuits. It relatesparticularly to circuits for translating pulses of differing amplitudesWithout altering the relative amplitudes of those pulses conveyingintelligence by reason of the amplitude variations thereof.

Circuit arrangements are known in which a variety of pulse type signalsare passed through amplifiers and mixers to finally terminate at autilization device at which the peak value of any signals must belimited to a certain value while all other smaller signals must have therelative Avalues maintained as far as amplitude is conltude pulsesoccurring therebetween at varying times, and with lesser and varyingamplitude values for display on some form of indicator such as akinescope.

If the peak amplitude of signals at the kinescope grid is to have amaximum value, then it would be advantageous to provide the amplier thatapplies the pulses to the kinescope with a good automatic gain control(A. G. C.) characteristic under all signal conditions.

The repetition rates of such peak pulse signals as commonly encounteredinpractice Varies between 60 C. P. S. to 15.75 kc. P. S. and the Widthof these pulses varies betwen .6 as. to 10 its. Thus there is a need forsignal translating circuit having an output peak value which will remainconstant for these conditions in response to an input peak value varyingas much as 5 to 1. l

There are many practical applications for this type of controlledamplifier. In some cases the gain of such an amplifier must be 10,000 ormore; in other cases unity gain is sufcient. Also, in some cases theinput of the amplier must be grounded, and insome cases the input mustbe 2 above ground with the A. G. C. voltage applic to the grid of therst tube.

There is a need for an A. G. C. circuit which can be used within allsuch pulse translator circuits, and because of the low gain encounteredin some of these ampliers, the A. G. C. circuit must have someamplification. Also, it must be able to work into an amplier gridresistor, whic is grounded or one that is ungrounded.

An object of the invention is to provide, in conjunction with othercircuits, automatic gain control for pulse translating systems whereinthe pulse repetition is variable over a Wide range 0I" values.

Another object of the invention is to provide, in conjunction with othercircuits, automatic gain control for pulse handling systems wherein theamplitude of certain peak pulses is limited to a predetermined valuewhile the amplitudes of other pulses are held only to the relativevalues.

A more specic object is to provide a novel circuit with Which tomodulate the amplitude of square waves or pulses.

Another specic object is to provide a novel circuit with which tooperate With additional circuits to produce D. C. amplification and lowfrequency amplification.

A further specic object is to provide a novel amplitude comparatorcircuit.

The objects of the invention are attained by means of a circuitarrangement comprising ua pair of controlled electron flow path orelectron discharge devices having a cathode impedance in common,individual output impedance elements connected in the anodes and arectier element connected between the anodes. A predetermined xedpotential is applied to the control electrode of one of the electrondischarge devices, and an alternating potential wave of substantiallyconstant frequency is applied to the control electrode of the otherelectron discharge device. This wave may be a sine wave, a sawtooth waveor almost any waveform, Ibut a square Wave is preferred. A low frequencyor a direct voltage wave is then applied, preferably but not necessarilyby way of an isolating device tor the control electrode of the same lastelectron discharge device to reproduce the alternating potential wavemodulated in amplitude bythe applied low frequency or direct voltagewave between the anodes of the electron discharge devices.

The invention is described hereinafter with reference to theaccompanying drawing forming part of the specification and in which:

Fig. 1 is a schematic diagram of a circuit arrangement according to theinvention incorporating a low frequency or direct voltage translatingcircuit, which in conjunction with other circuit provides A. G. C. foran amplifier carrying the types of signals previously described.

Fig. 2 is a graphical representation of the Waveforms developed' in' thecircuit arrangement of Fig. 1; and

Fig. 3 is another graphical representation of waveforms that may befound in the circuit when used as an amplitude comparator.

Referring to Fig. 1 there is shown in schematic form cascade-connectedvacuum tubes I2 and |3` and an output cathode follower lli', whichcomprise an example of a conventional pulse repeater or amplifier foramplifying a pulse signal wave of the type previously described. TheIsignal wave to be amplified is applied tov an input terminal I I and theamplified output signal wave isf obtained from output terminal I5. Thedesired' operation is obtained without automatic control of gain byconnecting both sets of terminals |1|8 and |9-20 in the grid circuits ofthe amplifier tubes I2 and I3 together respectively. By applying theproper automatic gain control voltages to either or both of these setsof terminals the gain can be varied inversely of the input or outputsignal amplitude in known manner. The known type of automatic gaincontrol circuit wherein a diode, a capacitor and a load resistor areconnected across the output terminalsv 2| and 22 to produce an automaticgain control voltage for application to either set of terminals |,1-I8or |9-2, is ordinarily of no practical value in pulse handling circuitsbecause the rectified D. C. voltage is not sufciently constant withrespect to the repetition rate of the peak pulses applied to inputterminals I I.

The proper automatic gain control bias voltage' for such an amplifiercircuit is provided according to the invention by the combination ofcircuit elements connected between the terminals 2|-22 and |1-|8.Essentially this circuit arrangement comprises an automatic slide-backpeak-to-peak reading voltmeter having the input connected to theamplifier load terminals 2'I-.22 and providing a directoutput voltage atthe terminals 25 and 26 proportional to the peak voltage amplitude ofthe recurrent video pulse supplied tothe output terminall I of theamplifier I0. A modulator element or repeater or a D. C. amplifiercircuit arrangement is connected to the terminals and 26 to produce anamplied pulsating output at the terminals 29 and 30, which outputvoltage is filtered by the lter connected between the terminals I1, I8and 29, 30.

Only the essentials of the automatic slide back vacuum tube Voltmeterare shown in Fig. l. A complete description of this type of Voltmeterincluding other desirable features will be had on referring to theProceedings of the IRE' for February 1947, in which there appears anarticle entitled An Automatic Slide Back Peak Voltmeter for MeasuringPulses, by C. J. Creveling and L. Mautner. The output of the Voltmeterat the terminals 25, 26 approaches the peak value of the highestamplitude pulse at the output terminals 2I-22 of the amplifier I0. Wherethe repetition rate and other characteristics of the of a common cathoderesistor 6|.

cuits of the amplifier tubes I2 and I3.

applied pulse train are suiciently constant, the portion of thepeak-reading Voltmeter between the circuit points PI and P2 may beomitted. An isolating resistor should be used to apply direct biaspotential to the grid of the tube 35.

The D. C. amplifier or repeater according to. the invention comprises afirst cathode follower triode 35 to the grid circuit of which the D. C.or low frequency potential appearing across terminals 25 and 26 isapplied. This triode is used mainly for isolating and impedance matchingpurposes, though other advantages may accrue as well. In the circuitshown, theorie megohm back-resistance of the diode 3|` serves as thegrid return but a resistor may be used if desired. The output of thetriode 35 obtained across the cathode resistor 39 is mixed with aconstant frequency recurring wave applied to the reference waveterminals II-:i2 and applied to the grid A1 of a triode vacuum tube 5I.The triode 5| is interconnected with a second triode 53. The cathodes 51and 59 are intercoupled and connected to a' source of negative voltageby means The anodes 65 and 61 of the tubes 5I and 53 respectively areconnected to a common source of positive potential through anoderesistors 1I' and 13 respectively and interconnected by means of a diodeelement 19. The diode element 19' may be connected in opposite directionif diodes |'0'I and |03 are reversed and a symmetrical Waveform atterminals lli-i2 is used asin Fig. 2. The grid 83 ofthe triode 53 isconnected toa source of positive potential by means of a voltage dividerarrangement comprising resistors 81 and |39. Preferably, the resistor 81is variable in order to adjust the ratio of the resistances and therebyvary the grid voltage applied to the reference grid 83. The anodes 65and 61 are connected to the output terminals 29 and 30 respectively bydirect current isolating capacitors 9| and 93. A diode element IUI isshunted across terminals 29- and 3|] and another diode element |03 isconnected in series with a resistor |05 between terminals I1 and 29. Aresistor III is connected between terminals I8 and 30. Capacitors II5.and |I1 interconnect the ends of resistors |05 and III to complete thefilter arrangement. A phase inverted amplified direct current of lowfrequency voltage proportional to the average amplitude of the lowfrequency or direct voltage applied to the terminals 25-26 is producedat the bias terminals |1-I8. If desired, the terminals I1 and I8 may beconnected together and the output of the filter connected to terminalsI9 and 20, the snorting link being removed, of course. Alternatively,another filter unit might be connected through blocking capacitorsbetween anodes 61 and 65 and I9-20, care being taken to prevent couplingbetween the grid cir- It is understood, of course, that any controlledelectron fiow path device, such as a transistor or a controllablesemi-conductor device, having emitter, control and collector elements,may be substituted for the evacuated electron discharge devices shown byfollowing the accepted design principles known to those skilled in theart.

The low frequency repeater circuit described is subject to the usualrule of modulation that the frequency of the wave applied at theterminals l5 |-2 must be at least twice the modulating frequency appliedto the terminals 25-23. A ratio of 5:1, ofcourse, will vafford betterresults and if a ratio of 10:1 Ior'greater'can be used, the 'l'ter 5design, when used as in Fig. 1, will be much easier. A simpleexplanation of the repeater for the two tubes 5| and 53 operating in aperfectly symmetrical circuit is as follows. Neglecting the effect ofrectifier 19, the potentiometer 81 is set to apply a predetermined valueof potential ec on the grid 83 of the tube 53. If a potential e1 equalto the potential ec applied to the grid 53 is applied to the grid 41 ofthe tube 5|, the anode potential of the tubes will be equal and therewill be zero voltage between plate 61 and plate 65 as shown by axis 29|,Fig. 2. If the potential e1 is greater than the potential ec the anode65 of the tube 41 will be more negative than the anode l$1 of the tube53. Likewise, if the potential ei is less than the potential ec, theanode 65 will be more positive than the anode 61. Still neglecting theeffect of the rectifier 19, a square wave voltage applied to theterminals 4| and i2 will result in the waveform represented by the curve2i3 at a of Fig. 2. Again neglecting the effect of the rectifier 19, alow frequency voltage waveform represented by the envelope curve 205,superimposed on the grid 41 of the tube 5| will produce a waveform asrepresented by the curve 201 at b. Taking into account the effect of therectifier 19, the waveform represented by the curve 2|() is obtainedbetween the anodes 65 and G1. The dashed lines above the curve 2li)indicate the pulse portions eliminated by the action of the rectifierelement 19. The normal bias voltage at amplifier l2 grid with no signalat input is zero. If the input at is zero, then the output at terminals2| and 22 is approximately zero. As previously explained, the action fof the slide back voltmeter should now produce a voltage at terminals 25and 26 of approximately zero, which means that with no signa-l at inputof amplifier I the average D. C. voltage at the grid i1 of tube 5| is inthe vicinity of zero. It is assumed, for simplicity, that when thesignal to input of amplifier I0 is zero, that the average D. C. voltageat the grid di of the tube 5| is zero. It was previously explained thatwhen the average D. C. voltage e1 at grid 41 of tube 5| is equal to theD. C. voltage ec at grid 83 of tube 61 all the square wave extendingabove axis 2Q! would be removed by the action of rectifier i9. It isobvious that if ec is increased more positive by varying resistor 81,that curve 2|!) could extend well above axis When this condition exists,rectiiier 19 locks anodes v61 and `(i5 at axis 20| and there is nosquare wave output at terminals 29 and 35. This is the normal operatingcondition for the circuit of Fig. 1 with no signal at input |I. If asmall signal such as a radar signal cf the type previously described isfed into ampliiier |53 at input Il, the signal will appear at terminals2| and 22. The slide back voltmeter circuit between p1 and p2 willdevelop a positive voltage at terminals and 26 corresponding to therecurring peak values of the signal at terminals 2| and 22 as previouslyexplained. This positive voltage at terminals 25 and 26 increases'positively the voltage e1 at grid 41 of tube 5|,

" ing to keepthe peak values of signal constant at i output |5 ofamplifier I0 after- -they have-reached a predetermined value as set bythe voltageec at the grid 83 of tube 53 as by resistor 81. The circuitbetween terminal 25-26 and |1|8 in this case is acting asa delayed D. C.amplifier Which in conjunction with slide back voltmeter constitutes adelayed A. G. C. circuit. In other words the signal at 2| and 22 mustreach a predetermined peak value before any bias at |1 and i8 isproduced to reduce the gain of amplifier |0. When the signal input toinput is above the predetermined value, as previously explained, anyincrease or decrease of recurring peaks of signal at input of ampliiiel`l0, which as explained above, cause the square wave to extend below axis23| as by curve 209 will cause the voltage at terminals i1 and I8 tovary as the average of the curve 209 and is represented by the curve2|i. The output at the bias terminals |1| 8 is a direct voltageproportional to the average filtered input at the terminals 29-30 whichdelivers substantially constant bias to the tube I2 varying only as theoutput voltage at the terminals 2|22 varies, which is the result ofsignal at input Il. The maximum direct voltage obtainable across thebias terminals |1-|8 for given operating potentials is the average valueof the wave applied at the terminals 4|-,42 multiplied by the gain ofthe circuit comprising the triodes {il-53.

Y The low frequency or direct voltage translating circuit arrangementVbetween the input terminals 25-25 and 4|-42 and the output terminals2-3|l is not limited to the application hereinbefore described but hasadditional advantageous applications as well. The circuit arrangementoffers a decided advantage as a remote gain control for a straight-sidedpulse amplier with grids at different D. C. levels. The input pulse waveis applied to the terminalsl ill-42 and the amplified pulse wave isobtained between ground and either one of the -anodes -61. A directvoltage is applied to the grid 41 either directly or preferably by acathode follower 55 to determine the desired operating conditions. Thegain of an amplifier can be adjusted remotely by changing the directvoltage applied at terminals 25--26- This voltage can easily be appliedat the end of a long direct current line without incurring serious ohmiclosses and without any stray coupling to the alternating current wavebeing translated by the circuit.

The circuit arrangement can be used as a re mote trigger phasingcircuit. A sawtooth Wave as represented by both of the curves 22| and225 of Fig. 3 is applied to the input terminals 4 i-t2. A wave,represented by the curve 22| alone, is taken ofi the terminals 2Q-3ii- Avariable weight square wave can be produced by putting output 29-30 intoan overdriven amplifier. That is, the per cent time one tube conductsout of the total period for one cycle, is adjusted as shown vby thecurve 221 by the value of direct potential applied to the terminals25-26. The trigger time is thus changed by a change in direct potentiallevel, which arrangement affords considerable accuracy to be obtainedwith relatively simple circuitry. By coupling a conventionaldifferentiating circuit to the output of the overdriven amplifier, apulse may be obtained at any time during the sawtooth period asrepresented by the curve 229 of Fig. 3.

The circuit arrangement shown in Fig. 1 between terminals 25-26 and |8|1was constructed and operated with the component parts values given belowforzuse with.a30..kc;/s.:square wave applied to terminals dll-42 andV0-500 c ./s. inputA wave to terminals 2 l-22- with 280 volts betweenground and they terminal marked +B, 160 V volts between ground and` theterminals marked and -150 Volts between ground and the terminals markedThe whole circuit arrangement of Fig. l was designed for a variablepulse rate of 60 c./s. 15.75 kc./s. with pulses varying in width from0.6 to ps. being translated through amplier IU. A square wave of kc./s.was then applied to ther terminals 4 |-42.

The invention claimed is:

1. In a pulse train translating circuit including a pulse train repeaterhaving input and output circuits, means incorporating automatic controlof gain, comprising a potential metering circuit coupled to said outputcircuit to develop a direct potential proportional to the potential ofthe pulses of said train at said output circuit, a direct current andlow frequency amplifier circuit having output terminals producing analternating potential in response to an alternating voltage wave appliedat one set of input terminals and arranged to modulate said wave inamplitude proportional to said direct potential obtained y from saidmetering circuit, and a rectier circuit coupled to the output terminalsof said direct current and low frequency amplifier circuit to produce adirect voltage proportional to the potential of the pulses of said trainat said output terminals, and means to apply said direct voltage to theinput circuit of said repeater in opposition to the amplitude variationsof said pulse train.

2. A circuit arrangement as defined in claim 1 and wherein the potentialmetering circuit develops a potential proportional to the peak amplitudeof the pulses of said train at the output circuit of said pulse trainrepeater.

3. A circuit arrangement as defined in claim l andwherein said inputcircuit of said pulse repeater comprises an electron ow path devicehaving at least electron emitter and electron control elements to whichsaid pulse train'is applied and to which said direct voltage is appliedto bias one ofv said elements with respect to the other.

4. A low frequency or direct voltage translating circuit arrangementcomprising a pair of electron now path devices having electron emitter,electron control and electron collector ele- -..ments,.an impedanceelement .cennected'n 0011?;

mon. to, said electron emitter elements, output impedance elements.individual to said electron collector elements, a rectifier elementlconnected between said electron collector` elements, means to apply apredetermined potential on the elec,- tron control element of one ofsaid electron flow path devices, means to apply an alternating potentialwave of substantially constant frequency to the electron control elementof the other of said electron flow path devices, and means to applyy alow frequency or direct voltage wave to the electron control element ofsaid other of the electron ow path devices thereby to reproduce saidalternating potential wave modulated by said low frequency or directvoltage wave at said electron collector elements.

5. A low frequency or direct voltage translating circuit arrangementcomprising a pair of electron flow path devices having electron emitter,electron control and electron collector elements, an impedance elementconnected in common to said electron emitter elements, output impedanceelements individual to said electron collector elements, a rectifierelement connected between said electron collector elements, outputcoupling devices capable of passing alternating current individual to`said electron collector elements, means to apply a predeterminedpotential on the electron control element of one of said electron flowpath devices, means to apply an alternating potential wave ofsubstantially constant frequency to the electron control element of theother of said electron flow path devices, and means to apply a lowfrequency or direct voltage wave to the electron control element of saidother of the electron flow path devices thereby to reproduce saidalternating potential wave modulated by said low frequency or directvoltage wave at said output coupling devices.

6. A low frequency or direct voltage translating circuit arrangementcomprising a pair of electron discharge structures having cathode,control and anode electrodes, an impedance element connected in commonto said cathode electrodes, output impedance elements individual to saidanode electrodes, a rectifier element connected between said anodeelectrodes, means to apply a predetermined potential on the controlelectrode of one of said electron discharge structures, means to applyan alternating potential wave of substantially constant frequency to thecontrol electrode of the other of said electron discharge structures,and means to apply a low frequency or direct voltage wave to the controlelectrodes of said other electron discharge structure device thereby t0reproduce said alternating potential wave modulated by said lowfrequency or direct voltage at anode electrodes.

'7. A low frequency or direct voltage translating circuit arrangementcomprising a pair of electron discharge structures having cathode,control and anode electrodes, an impedance element connected in commonto said cathode electrodes, output impedance elements individual to saidanode electrodes, a rectifier element connected between said anodeelectrodes, means to apply a predetermined potential on the controlelectrode of one of said electron discharge structures, means to applyan alternating potential wave of substantially constant frequency to thecontrol electrode of thel other of said electron discharge structures,and means to apply a low frequency 0r direct voltage wave to the controlelectrode of said other electron dischargeV structure, thereby .tQrenrqduce Said alternating Roten- 9 tial wave modulated by said lowfrequency or direct Voltage wave at said anode electrodes.

8. A low frequency or direct voltage translating circuit arrangementcomprising a pair of electron flow path devices having electron emitter,electron control and electron collector electrodes, an impedance elementconnected in common to said electron emitter electrodes, outputimpedance elements individual to said electron collector electrodes, arectifier element connected between said electron collector electrodes,output coupling devices capable of passing alternating currentindividual to said electron collector electrodes, means to apply apredetermined potential on the electron control electrode of one of saidelectron ow path devices, means to apply an alternating potential waveof substantially constant frequency to the electron control electrodesof the other of said electron flow path devices, and means to apply alow frequency or direct voltage wave to the electron control electrodeof said other of the electron flow path devices, a diode element coupledto both of said output coupling devices, lter impedance element andanother diode element connected in series to one of said output couplingdevices, another filter impedance element connected to the other outputcoupling device, and reactive impedance elements bridged across saidlter impedance elements.

9. A low frequency or direct voltage translating circuit arrangementcomprising a pair of electron discharge structures having cathode,control and anode electrodes, an impedance element connected in commonto said cathode electrodes, output impedance elements individual to saidanode electrodes, a rectier element connected between said anodeelectrodes, means to apply a predetermined potential on the controlelectrode of one of said electron discharge structures, means to applyan alternating potential l@ wave of substantially constant frequency tothe control electrode of the other of said electron dischargestructures, means to apply a low frequency or direct voltage wave to thecontrol electrode of said other electron discharge structure devicethereby to reproduce said alternating potential wave modulated by saidlow frequency or direct voltage wave at anode electrodes, and directcurrent isolating impedance element coupled vtial wave of substantiallyconstant frequency to the control electrode of the other of saidelectron discharge structures, and a cathode follower circuit arrangedto apply a low frequency or direct voltage wave to the control electrodeof said other electron discharge structure device thereby to reproducesaid alternating potential wave modulated by said low frequency, ordirect voltage wave at anode electrodes.

HOWARD MULDER SCOTT.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,519,359 Dean Aug. 22, 1950 2,585,883 Wendt et al Feb. 12,1952 Lawson et al. Jan. 6, 1953

